My book shows that there were 670 gas and LP G900s made from 1967 through early 1969. They were all serial numbered together for both fuel types. In late 1969, the LP models got a separate serial numbering convention, and 160 of those were made. So, yes, a gasoline G900 is fairly low production.
I have two G900s. One is an LP and the other is a diesel. Either is fairly easy on fuel on lighter jobs, and both will suck the fuel when the load has the governor held against the stop, just as one might expect. Both of mine have three point lifts and dual PTOs. I wouldn't take $3500 for either of them. They are worth more than that to me since I use them. Good tractors.